Examination of variability among the salivary proteomes of Diuraphis noxia biotypes

Russian Wheat Aphid (Diuraphis noxia Mordvilko, RWA), an economically important pest of wheat and barley worldwide, has several recognized biotypes. These biotypes, classified according to their differential abilities to overcome the host resistance encoded by several loci in wheat and barley, have not previously been distinguished from one another molecularly. We have demonstrated the presence of differential expression among the salivary proteomes of RWA biotypes 1,2,5, and 8 by 1-D and 2-D gels, and by MS/MS analysis of in-solution digests of RWA salivary extracts. Both qualitative and quantitative differences within the salivary proteomes of the studied biotypes were observed in 1-D and 2-D gel analysis. MS/MS analysis putatively identified with very high confidence several proteins, including glucose dehydrogenases, apolipophorins, N-acetyl glucosaminidase, actin-binding and depolymerizing proteins, trehalase, and the calcium-binding proteins calreticulin and a-catulin. These identities represent approximately 10% of the total RWA salivary content, based upon 2-D spot counts. The identified proteins fit well with the model of aphid virulence, in which the host resistance response is subverted by the action of aphid salivary proteins. While a more complete profile of individual salivary proteins will require an expansion of RWA genomic and transcriptomic databases, this work represents an important step in the identification and analysis of the RWA salivary proteome.